Ink jet printing processes are essentially of two types:
In continuous stream ink jet printing systems, ink is emitted in a continuous stream under pressure through a nozzle. The stream breaks up into individual droplets at a certain distance from the nozzle. If a specific location on the recording sheet has to be printed the individual droplets are directed to the recording sheet, otherwise they are directed to a collecting vessel. This is done for example by charging unnecessary droplets in accordance with digital data signals and passing them through an electrostatic field which adjusts the trajectory of these droplets in order to direct them to the collecting vessel. The inverse procedure may also be used wherein uncharged droplets end up in the collecting vessel.
In the non-continuous process, or the so-called “drop-on-demand” systems, droplets are generated in accordance with digital data signals only if a specific location on the recording sheet has to be printed.
The speed of ink jet printers of the newest generation is ever increasing for economic reasons. Digital images, captured with digital cameras or generated by scanning of silver halide camera films, may be printed with these modern printers at a quality level that makes these images nearly indistinguishable from classical copies on silver halide materials. Images produced in this way need to have an excellent storage stability even under adverse conditions. This can only be achieved by using a finely tuned system of inks (respectively the dyes contained therein) together with a suitable recording sheet.
Recording sheets particularly suitable for these printers and photo realistic recordings need to absorb the inks very rapidly. The recording sheets comprise organic polymers and/or microporous inorganic oxides. Up to now the produced images do not have all the properties required. Particularly the brilliance of images printed onto such recording sheets is unsatisfactory. Therefore, there is a need for dyes in order to increase especially the brilliance of red and magenta colors of images printed onto these recording sheets.
Although quite a number of different dyes have already been proposed as dyes for ink jet printing, none meets all the necessary requirements.
The magenta dye of formula (I) (Example No. 2) is described in U.S. Pat. No. 5,542,970 to Miura et al. 
The magenta dye of formula (II) (Example No. 1) is described in patent application EP 0,918,074. 
The magenta dye of formula (III) (Example No. 1) is described in patent application JP 03-203,970. 
All these dyes, representing the state of the art, do not satisfy all the required demands if they are used in the formulation of inks for ink jet printing that should provide magenta images or colorings with particularly brilliant bluish hues on any type of recording sheet as plain or coated paper, coated or uncoated, opaque or transparent synthetic materials (elevated negative values of b* in the L*a*b* system).
Dyes used for such inks need to have a good solubility in the essentially aqueous ink liquid, they have to penetrate into the recording sheet and should not show dye aggregation on the surface of the recording sheet (“bronzing”). They need to provide printed images having high optical density, good water fastness, good light stability and good storage stability even under adverse conditions. They need to be stable in the ink even when the ink is stored for a long time under adverse conditions.
Various types of compositions have been proposed as inks. Typical inks comprise one or more dyes or pigments, water, organic cosolvents and other additives.
The inks have to meet the following criteria:                (1) The ink gives images of excellent quality on any type of recording sheet.        (2) The ink gives printed images exhibiting good water fastness.        (3) The ink gives printed images exhibiting good light stability.        (4) The ink gives printed images exhibiting excellent smudge behavior.        (5) The ink gives printed images exhibiting excellent storage stability under conditions of high temperature and humidity.        (6) The ink does not clog jetting nozzles of the ink jet printers even when these are kept uncapped while recording is suspended for long periods.        (7) The ink may be stored for long periods of time without deterioration of its quality.        (8) The values of the physical properties of the inks, such as viscosity, conductivity and surface tension are all within defined ranges well suited for the intended use.        (9) The ink has to be non-toxic, not flammable and safe.        